An 18-year-old gunman has opened fire at an elementary school in the US state of Texas, killing at least 19 children and two teachers as he went from classroom to classroom, before being shot dead by police.

The assault at Robb Elementary School in the small town of Uvalde was the deadliest shooting at a school in the United States since a gunman killed 20 children and six adults at Sandy Hook Elementary in Newtown, Connecticut, in December 2012.

Hours after the attack, families were still awaiting word from their children.

Outside the town civic centre, where relatives were told to await news about their loved ones, the silence was broken repeatedly by screams and wailing. “No! Please, no!” one man yelled as he embraced another man.

“My heart is broken today,” said Hal Harrell, the school district superintendent. “We’re a small community, and we’re going to need your prayers to get through this.”

Adolfo Cruz, a 69-year-old air-conditioning repairman, was still outside the school at sunset, seeking word on his 10-year-old great-granddaughter, Eliajha Cruz Torres.

He drove to the scene after receiving a terrifying call from his daughter shortly after the first reports of the shooting. He said other relatives were at the hospital and the civic centre.

Waiting, he said, was the heaviest moment of his life.

“I hope she is alive,” Cruz said.

The attack came just 10 days after a deadly, racist rampage at a supermarket in Buffalo, New York that added to a yearslong series of mass killings at churches, schools and stores.

In an address to the nation hours after the Texas school attack, President Joe Biden made an emotional appeal calling for new gun restrictions.

“As a nation, we have to ask, when in God’s name are we going to stand up to the gun lobby? When in God’s name are we going to do what has to be done?” Biden asked. “Why are we willing to live with this carnage?”